Microwave receivers employ various techniques to establish a predetermined point, referred to as a threshold, that is used to start the operation of detecting and encoding selected parameters of received RF signals which comprise a coherent RF carrier and wide-band noise. Typical parameters include RF frequency, RF amplitude and pulse width, and all of which should be accurately encoded in order to preserve the integrity of the system performance. Further, the threshold level for detecting these parameters should also be accurately established. Erroneous determination of the threshold level may either render the receiver insensitive to all signals, or cause the receiver to erroneously trigger in the absence of an RF signal. Either event is not desirable.
Techniques commonly employed to determine the threshold level have generally depended on the establishment of the receiver threshold level based on a time average of noise measurements in the receiver, or based upon an external processor empirically setting the threshold by using a history of receiver false alarm events. In a particular case, known as a digital noise-riding threshold, the microwave receiver continuously samples the noise level within the receiver, averages these samples, adds an offset acting as a safety factor and, then, uses the results to determine the receiver's threshold. Typical sampling intervals cover approximately three milliseconds with updating of the threshold data occurring at the end of each sample interval. Samples are collected only in the absence of the RF signal because to do otherwise would have the threshold level riding on the RF level, rather than on the noise. Even in the absence of the RF signal, because of the integration time of the circuit operation, it may take the microwave receiver as long as six milliseconds to respond to a change in the noise level in its determination of the threshold level.
The prior art used to establish the threshold level seems to suffer from the drawbacks of sampling techniques that consume a relatively large amount of time, such as six milliseconds, and that need to be performed in the absence of RF signals.
It is, therefore, a primary object of the present invention to provide for a circuit arrangement that substantially instantaneously establishes an accurate threshold in the presence of received RF signals.
It is another object of the present invention to provide for a circuit arrangement that establishes a threshold level that takes into account the signal to noise ratio (SNR) of the received RF signals.
It is a further object of the present invention to provide for a circuit arrangement that yields accurate angle data that may be used in the determination of the frequency parameter of the received RF signal.
Other objects of the present invention, as well as the advantages thereof over existing and prior art forms, which will be apparent in view of the following detailed description are accomplished by means hereinafter described and claimed.